There have been proposed a number of amorphous silicon system light receiving members. They have been evaluated as being suitable as electrophotographic light receiving members for use not only in high speed electrophotographic copying machines but also in laser beam printers since they are high in surface hardness, highly sensitive to a long wavelength light such as semiconductor laser beam (770 nm-800nm), and hardly deteriorated even upon repeated use for a long period of time.
FIG. 3 is a schematic cross section view of a typical configuration of such amorphous silicon system light receiving member, which comprises an electroconductive substrate 301 made of a proper material such as aluminum and a light receiving layer comprising a charge injection inhibition layer 302 capable of preventing injection of a charge from the side of the substrate 301, a photoconductive layer 303 exhibiting photoconductivity and a surface protective layer 304.
The image formation using said light receiving member is carried out, for example, in the following manner by using an appropriate electrophotographic copying machine as shown in FIG. 4.
FIG. 4 is a schematic explanatory view of the constitution of a conventional electrophotographic copying machine. As shown in FIG. 4, near a cylindrical light receiving member 401 having the configuration shown in FIG. 3 which rotates in the direction indicated by an arrow, there are provided a main corona charger 402, an electrostatic latent image-forming mechanism 403, a development mechanism 404, a transfer sheet feeding mechanism 405, a transfer charger 406(a), a separating charger 406(b), a cleaning mechanism 407, a transfer sheet conveying mechanism 408 and a charge-removing lamp 409.
The cylindrical light receiving member 401 is maintained at a predetermined temperature by a heater 423. The cylindrical light receiving member 401 is uniformly charged by the main corona charger 402 to which a predetermined voltage is impressed. Then, an original 412 to be copied which is placed on a contact glass 411 is irradiated with a light from a light source 410 such as a halogen lamp or fluorescent lamp through the contact glass 411, and the resulting reflected light is projected through mirrors 413, 414 and 415, a lens system 417 containing a filter 418, and a mirror 416 onto the surface of the cylindrical light receiving member 401 to form an electrostatic latent image corresponding to the original 412.
This electrostatic latent image is developed with toner supplied by the development mechanism 404 to provide a toner image. A transfer sheet P is supplied through the transfer sheet feeding mechanism 405 comprising a transfer sheet guide 419 and a pair of feed timing rollers 422 so that the transfer sheet P is brought into contact with the surface of the cylindrical light receiving member 401, and corona charging is effected with the polarity different to that of the toner from the rear of the transfer sheet P by the transfer charger 406(a) to which a predetermined voltage is applied in order to transfer the toner image onto the transfer sheet P. The transfer sheet P having the toner image transferred thereon is electrostatically removed from the cylindrical light receiving member 401 by the charge-removing action of the separating corona charger 406(b) where a predetermined AC voltage is impressed and is then conveyed by the transfer sheet conveying mechanism 408 to a fixing zone (not shown). The residual toner on the surface of the cylindrical light receiving member 401 is removed by a cleaning blade 421 upon arrival at the cleaning mechanism 407 and the removed toner is discharged by way of waste toner discharging means (feed-screw) 423. Thereafter, the thus cleaned cylindrical light receiving member 401 is entirely exposed to light by the charge-removing lamp 409 to erase the residual charge and is recycled.
The amorphous silicon system light receiving member to be used in the image-forming process as above described has such advantages as above mentioned, for example, it exhibits a high sensitivity against a long wavelength light (sensitivity peak near 680 nm and sensitivity region of 400 to 800 nm), and it is practically satisfactory since practically acceptable images without accompaniment of crushed line image or slim line image can be reproduced as long as ordinary documents are copied. However, it is not sufficient enough to meet a recently increased demand to provide a high quality image equivalent to a printed image obtained by a printing machine.
That is, when an original containing superfine lines of 100 .mu.m or less in width is reproduced by the foregoing image-forming method using such amorphous silicon system light receiving member as above mentioned, there often appear undesirably fattened lines or undesirably slimmed lines on the resulting copied lines. Likewise, when an original containing complicated Chinese characters (KANZI in Japanese) of 2 mm or less in size is reproduced by the foregoing image-forming method, the resulting copied chinese characters often have crushed line images or slim line images which can not be easily distinguished.
Therefore, it is generally recognized that the foregoing image-forming method using an amorphous silicon system light receiving member is not suitable for reproducing such originals as above mentioned, for example, catalogs or manuals of articles for sale, etc., mainly because of insufficient resolution.
The foregoing problem is apparently caused when the image-forming method is practiced under high humid environment. In order to eliminate this problem, there has been proposed a method of heating the amorphous silicon system light receiving member. However, it is still difficult to obtain desirable copied images from such originals containing superfine lines or complicated Chinese characters.
Independently from what above described, there is another disadvantage for the foregoing image-forming method using an amorphous silicon system light receiving member that a certain quantity of ozone or reaction products (such as nitrogen oxides, etc.) caused by ozone is generated because of corona charging. The quantity of ozone to be generated is in proportion to the amount of electric current to be applied onto the charger. And the quantity of ozone to be generated in the case of negative charge is 5 to 10 folds greater over that in the case of positive charge.
In order to prevent leakage of ozone to be generated into the outside of the system, the system is provided with an activated carbon filter (not shown in the figure), by which the ozone is adsorbed or decomposed so that the air exhausted from the system contains 0.1 ppm or less of ozone.
However, there is an increased social demand to further decrease the ozone content in the air exhausted from the system because of the spread of electrophotographic copying machine not only in offices but also in private houses.
The ozone generated in the electrophotographic copying machine is a problem for an amorphous silicon system light receiving member installed therein because the ozone and the reaction products caused as a result of reacting with air are adsorbed on the surface of the light receiving member. As a result chemical reactions among the ozone, the reaction products and the constituent materials of said surface occur and the characteristics of the light receiving member are undesirably changed. This leads particularly to reducing the resolution. This situation is significant in the case of practicing the image-forming method using an amorphous silicon system light receiving member which has been repeatedly used under highly humid environment.